Industrial robots have become an indispensable part of modern manufacturing. Whether transferring semiconductor wafers from one process chamber to another in a cleanroom or cutting and welding steel on the floor of an automobile manufacturing plant, robots perform many manufacturing tasks tirelessly, in hostile environments, and with high precision and repeatability.
For safety, and to prevent damage to a robot arm and/or a robotic tool attached to it, crash protector devices are known in the art. A crash protector device is interposed between a robot arm and a robotic tool for detecting and indicating a crash condition, defined as an excessive force or torque applied to the robotic tool, usually as a result of unintended contact. The crash protector device exhibits a predetermined compliance, or allowance of relative movement between the robotic tool and robot arm, prior to indicating a crash condition. The crash condition indication may comprise an electronic signal sent to a robotic controller, which may halt movement of the robotic arm in response, to prevent further damage. The crash protector device mechanically and electrically resets itself when the crash force is removed.
It is desirable for the robot crash protector operation to be rotationally invariant. That is, ideally the same force should result in the same crash protector operation (that is, being within the compliance range or indicate a crash condition) regardless of the radial direction in which the force is applied. In practice, prior art robot crash protector devices exhibit radial variations in the amount of force necessary to trigger a crash condition indication.
FIGS. 13 and 14 depict the moment and angle of deflection, respectively, at crash detection of a prior art crash protector device, for forces applied at radial positions 30° apart. FIG. 13 graphs the force moment that generated a crash condition indication at each indicated radial angle. FIG. 14 graphs the angle of deflection of a portion of the crash protector device attached to a robotic tool, with respect to a portion of the device attached to a robotic arm, at crash condition indication for a force applied at each indicated radial angle. Crash protector devices are made in different sizes, and many have adjustable operating parameters, such that the magnitude of the graphed force values may vary. However, regardless of the magnitude of the applied force required to indicate a crash condition, the crash protector device should ideally show little or no variation in force magnitude or deflection angle at crash condition indication as the crash force is applied in any radial direction. Inspection of FIGS. 13 and 14 indicates significant variation of both required force and deflection angle as the crash force is applied in different radial directions around the axis of the crash protector device.
Additionally, many prior art robot crash protector devices require manual adjustment of internal parts, such as switch assemblies, to achieve acceptable crash protector operation. Manual adjustments increase manufacturing costs and decrease reliability of the crash protector device.